Punch and Die Tolerance?

[Tiggy_dorset]

I have been given a machined punch and die to harden and anneal. Before commencing, I thought to 'obviously' be sure that they mate with each other and slide. Alas! I cannot get them to fit together, so I measured them. The punch is 0.04mm smaller that the die, but is too tightly toleranced to get to fit. What is the general tolerance one should expect for a punch and die?

The punch is a lump in comparison to the thin walled die. After hardening and annealing should I expect the final size to be diffent to pre hardening/annealing, ie. will expand or shrink?

 

[awemawson]

Punch clearance is a function of material type and material thickness, much like setting the clearance on a guillotine. Seem to remember somthing like 15% of material thickness for steel - this may help:

http://www.unipunch.com/TechSupport/DieClearance/DieClearanceCalculator.aspx

 

[Tiggy_dorset]

Thanks, thats a handy link.
Now just the question of whether the tolerances will differ between pre and post heat treatment.

 

[Normsthename]

On a CNC Punching machine the Die is 20% larger of the material being punched.
So a 10mm Diameter punch on 1mm thick material would be 10.2mm and on 3mm material the die would be 10.6mm
Hope this helps.

Andy

 

[Tiggy_dorset]

Yes it does, clearly the customer hasn't taken this into account. I will go back to them and possibly give them the link for reference. It was lucky I checked as I was all set up ready to fire the oxy/acet. Without checking, I would have had no idea whether the heat treatment had affected the fit or not.

 

[I'm getting on a bit]

If you were making a washer say

The punch for the hole would have the clearance in the die

For the outer diameter the clearance would be on the punch

 

[AndersK]

Wont they grind into tolerance and polish the dies after heat treatment?

 

[Bill Edwards]

I'm not an expert on heat treatment, but for rough work/tools there isn't a significant change to the size.

However, anything that has to be exact gets ground after treatment. There probably are small changes and items can sometimes warp if the cooling isn't even, and grinding the part afterwards is done for the required finish and tolerance.

I think that in the case of the punch and die it is either going to be ground after treatment or an error has been made.

 

[Sidewinder]

Having worked in a toolroom heat treatment shop, I would say that they have left an allowance for finishing on the parts, on the punch for finish grinding, because the oxidation post heat treat will be no use for use IYKWIM.
The die, the same, but possibly an allowance for sparking after heat treatment.

 

[Tiggy_dorset]

That all makes a certain sense. I will question the customer on Monday before progressing, to be sure. Ill post the outcome.
Thanks.

 

[Tiggy_dorset]

The customer is aware of the tight tolerance and said it was for punching out thin plastic sheet. He said they plan to polish it out to fit.
He also said he will put the work my way if they make more that require hardening.